Safety device for lifting mechanism



5 Sheets-Sheet 1 Wuj J B HARRISON ETAL SAFETY DEVICE FOR LIFTIN G MECHANISM July I, 1952 Filed Jan. 13, 1951 July 1, 1952 J. B. HARRISON ET AL 2,601,759

SAFETY DEVICE FOR LIFTING MECHANISM Filed Jan. 15, 1951 5 Sheets-Sheet 2 [III/A July 1, 15352 J. B. HARRISON ET AL SAFETY DEVICE FOR LIFTING MECHANISM Filed Jan. 13 1951 5 Sheets-Sheet 5 m 9 u J M w d J s M v m W J. wivrifidn M W N J. 0J0 a 4 J 8 m U M. 7 a m m G I I J p a A V E ,m 3 L w P M L a 1 2 A 3 3 J m y H]. 5 H N 6 W 2 w .4 o 5 111/. M y 1 a H H H jmd? 755 Patented July 1, 1952 UNITED STAT SAFETY DEVICE ron LIFTING'MECHANISM John. B. Harrison and Lawrence F. Jaseph,

Memphis, Tenn, assignors to Rotary Lift Company, Memphis, Tenn., a corporation of Delaware ' Application January 13, 1951, Serial No. 205,904

12 Claims.

Our invention relates generally to safety devices for liftingmechanismsand more particularly to mechanisms of. this character for use with hydraulic lifts of the two-post type having movementequalizing means.

a It is frequently desirable to provide more than one hydraulic ram in a. lifting mechanism for heavy objects,- and in such apparatus it is desirable to provide equalizing means to make certain that the severalrams'will. be elevated and lowered at the same rate with the result that. the platform or other support carried by the upper ends of the ram plungersiwillremain level at all times. In. such apparatus, it is also highly desirable to provide safety means to prevent lowering of theplungers and theload carried thereby, should the hydraulic pressure operating onthe plungers fail. This. is particularly true in lifts for heavy. devices. for the emission of radiant energy'in the treatment of pathological conditions, where. theheavy apparatus must. be suspended over thepatient. .The invention is therefore di sclosed herein as applied to a. lifting mechanism the manual. controlsv are. operated to lower the load. M i

A: further objectis to provide an improved lifting mechanism having an improved safety device and control circuits, which are simple in construction, reliable in operation, and which may be economically manufactured.

Other objects will appear from the following description, reference being had to the accompanying drawings, in which;

Fig; 1 is an .elevational view of the lifting mechanism; a

Fig. 2 is a planview thereof;

Fig.3 isan enlarged fragmentary detail, partly sectionalized, showing one of the plungersand the manner of anchoring. the equalizing chains;

Fig. 4 is a sectional viewtaken on the line 4 l OfIFig; 3;

Fig. 5 is a horizontal sectional view. taken onthe lines 55 of Figs. 1 and 3; 1 3

Fig. B-is a fragmentary sectional view taken-on the line 6-6 ofyFigl, showing the parts to an enlarged scale;

Fig. '7 is. a broken sectional View taken generally alongthe line 'l-.-'! of Fig. 6;

Fig. 8 is afragmentarysectional view taken on theline 8--8 of Fig. 1; i

Fig.9. is a fragmentarysectional view taken on the. line 9'9 of Fig. 1 and Fig.10 is ahydraulic and electrical circuitcliagram of the controls for the lifting: mechanism.

. Referring toFigtl, the lifting mechanismc omprises apair of: cylinders I0 and H- suitably sehand plunger. guiding structure.

cured in' th building foundation [2 andsecured respectively. to the walls 14 and I5, by means including brackets l3. Plungers. l6 and l'l arenrespectively reciprocable in the cylinders ID and l I, being supplied with hydraulic operating fluid under pressure in a hereinafter to be described manner, through conduits l8 and; 19 connected to suitable control valves, and a source of; hydraulic fluid. l

.A box-section load supporting beam is: fab! ricated from suitable: channels 2| and plates 22, as best shown in Fig. 8, the partsbeing welded together to form a unitary structure. Theends of this beam are suitably secured to the upper endslof the rams or plungers l6 and I'hrespectively, as :best illustrated in Figs. 6 and 7; Each ofthe plungers is guided for rectilinear movement by a pair. of rails 24, 25, which are welded or 0th.- erwise secured to vertical channels 26 and 21; .respectively; and the latter are secured to the walls I 4 and; by a plurality of brackets 28.

Each of the rams and its guides and supporting structure are partly'enclosed by a suitable sheet metal housing 30. The'channe1s'26, 21 have a chain anchor bar 32 rigidly secured thereto, asby welding, and their upper ends support a cap plate 36'provided with suitable reinforcing plates 38, 39 and4'fl, the plate 40 being suitably secured to the wall (5. hand-plunger guide structure forms a support for the end of a chain A, the end-of'the latter-being secured toa stud 42 provided with an adjusting nut ,while the cap plate 36 of the left hand plunger guide structure serves similarly as a support for the: anchoring adjustable stud 46 secured to a' chain B,.the. other end of chainuB being secured to theanchoring bar 32rof the right In a similar manner the other endof chain A is anchored to ananchoring. bar 33 of the guide structure. for the left handplunger.

As best x shown in Figs. 6 and 7 thebeam chanl- The cap plate 36 of the right 3 nels 2I have collars 48 and 49 secured thereto for the reception of a fixed shaft 50 having shoes 52 and 53 pivoted at the ends thereof, the shoes engaging guide rails 24 and 25 respectively. The shaft 50 for the right hand plunger has a pair of sprocket wheels 55, 51 secured thereto for engagement with chains A and B, respectively. These sprocket wheels are rigidly secured together and to ratchet wheels 58 and 59 by a plurality of studs 60, the sprocket wheels being suitably spaced by a ring 62 and thus firmly clamped to the ratchet wheels 58 and 59. The ratchet wheels 58 and 59 are provided with counterbores for the reception of bearing bushings 64 for engagement with the fixed shaft 50.

A two-toothed pawl 00, engageable with the ratchet wheel 58, is pivoted on a stub shaft 68 which is suitably secured in a pair of bracket plates I which are in turn secured to a beam end plate [2 and a reinforcing and mounting plate I4. A- pawl 15, similar to the pawl 66, is similarly mounted for engagement with the ratchet wheel 59. The pawl 06'is adapted to be disengaged from the ratchet wheel 58 by a solenoid I8, the upward stroke of the pawl being limited by an adjustable locked screw 80.

The plates 14 serve as a support for a normally open switch 82 preferably having a roller arm 84 for engagement with the pawl 66, the switch being; adapted to be closed when the pawl 06 is fully disengaged from the ratchet wheel 58.

Similarly, the pawl 0'! is provided with an actujating solenoid 19 (not shown in Figs. 6 and 7) and is adapted to close a switch 83, in the same teeth out of alignment to the extent of one-half the tooth pitch, to reduce lost motion.

At the upper end of the left hand plunger there is 'a' sprocket and bearing construction similar. to that shown in Figs. 6 and 7 except that the ratchet wheels 58, 59, pawls 58 and 61, solenoids 18,19, and switches 82, 83, together with their mountings, are omitted. These parts could be included except for the advantageous reduction in cost resulting from their omission. The manner in which the chains A and B pass around the sprockets at the upper ends of the plungers is indicated in Fig. 1, it being understood that these chains operate in more or less conventional manner to assure that the plungers I and I? are raised and lowered at the same rate, and thus that the beam is maintained horizontal at all times.

' .The load which is raised and lowered by the lifting mechanism is illustrated as comprising a radiation emitting apparatus 90 which is supported, asbest indicated in Fig. 8, by a pair of angle shaped saddles 92, 93 which are welded together and rest upon shim plates 94 and 95 'v'vhich'in turn rest upon the top plate 22 of the beam section. Tension bars 96 and 91, together with housing plates 98, are .secured to the saddle angles 92, 93 by studs I00. Keys I02 and I03 fitting closely in suitable complementary grooves formed in the tension bars and the saddle angles, provide anadditional weight bearing 4 connection between the saddle 92, 93 and the load supporting tension bars 96 and 91. A sheet metal duct I06 is suitably secured to the beam plate 22 of the beam to cover conductors leading to the radiation emitting apparatus 90.

In the event that remote indication of the degree of elevation of the apparatus is required, a self-synchronous three phase generator with single phase excitation may be mounted within a suitable housing I08 and geared,

through a speed increasing gearing, to the adjacent sprockets over which the chains A and B pass, and the output of this generator supplied to a remote self-synchronous receiver. which operates in synchronism with the generator, and is geared to a suitable indicator.

Suitable hydraulic and electric controls are provided for the operation of the lifting mechanism, these including, as best shown in Fig. 9, a down limit switch LSD, an upward travel limit switch LSU, and a safety limit switch LSS mounted upon channel 21. These switches are adapted to be operated by a cam IIO which is suitably secured to the beam 20.. These three limit switches are of conventional construction, having roller bearing arms II2 which, when engaged by the cam IIO, are swung counterclockwise to open their contacts. In other words, these are normally closed contacts.

These limit switches are connected in a control circuit as diagrammatically illustrated in Fig. 10. Main current supply conductors LI, L2, and L3 are adapted to be connected to'a power line by closing a main switch H6. A motor H8 is adapted to be connected to these power lines upon closure of contacts UI, U2, and U3. A pair of overload relay heaters OL are connected respectively between the contacts UI and U2, and the motor H8. The motor II8 drives a pump I20 which draws oil or other suitable hydraulic actuating fluid from a reservoir I22 and delivers it to a discharge pipe I24, the pressure in the latter being prevented from exceeding a predetermined maximum value by a spring loaded pressure relief valve I26. A check valve I28 is connected between conduit I24 and conduit I30 to prevent reverse flow from the lift cylinders I0 and II, the conduit I30 being connected to these cylinders by the conduits I8 and I9.

Thus, when the motor H8 is energized, hydraulic fluid under pressure is supplied. to the cylinders I0 and II to force the plungers I6 and I1 thereof upwardly. When the plungers. are to be lowered at normal speed, a solenoid I32 is energized to open a valve I34 which permits oil to flow from the cylinders to the reservoir I22 at a rate which may, if desired, be controlled by a restriction I36. When the lift is to be lowered slowly, a solenoid I38 is energized to open a valve I40 which permits flow from the plunger cylinders through a restriction I42 to the reservoir I22. The restriction I42 may be fixed or variable, depending upon the character of operation desired.

It is believed that the electrical control circuits may best be described in conjunction with a description of the operation of the various parts through a complete cycle. 1

Assuming that the lift is in lowered position and that it is desired to raise it, an Up push button is operated to close contacts MI and thereby complete a circuit through a relay coil UA which is in series with normally closed'contacts DI, SI, LSU, andLSS across the lines LI and L3. Energization of relay UA causes closure of its normally openl contacts UAI and ,II, thus raising the plungers, at a rate determined by the capacity of; the pump I20.

Ifpit is desired to arrestthe upward movement at; any time, it is necessary merely to release the push. button I4Ij, which, through deenergization of relay U, cuts off supply of current to the motor I I8. The, check valve I28 will normally maintain the plungers in the elevated position, but if, due to, any slight leakage in the system, there is a tendency for the'plungers, to drift downwardly, one of the pawls 66,, 61 will, after downward movement of but a short distance, engage the teeth of its ratchetwheel 58 or 59, and thereby stop further downward movement. Since the teethof the ratchet wheelsare spaced apart by one-half a tooth, the maximum distance that the lift may descend under these conditions is very small. If the operator maintains the Up pushbutton contacts 1 4I closed, limit switch LSU will open as the lift reaches the normal upper limit of its travel, and thus, through deenergization of relay UA, will open contacts UAI and thereby deenergize relay U and stop the motor I28. If for some unforeseen reason the limit switch LSU, or anyother part of the related circult, elements, fails to operate and the lift moves beyond its normal upward limitof travel, the cam III) will operate the safety limit switch LSS to open its contacts, thus deenergizing. all of the control circuits and necessarily. stopping, the operation of the motor II8.

Assuming that the lift has now been raised and it is desired to lower it, the operator will depress the Down. push button, thereby closingswitch I46 and, completing a circuit through thedown valve solenoid. I32, which circuit may be traced asfollows: From LI, push button contacts I46,

solenoid I32, conductor I41, switches 82 and 83, cows, limit switchLSD, contacts UA2, conductor Switches 82 jand 83, it. will be recalled, are closed, only when 148; limit. switch LSS, to line L3.

the pawls-Stand 61, respectively, are intheir elevated positions due to energization of the solenoids I8, and. I9,,respecti,vely. These solenoids are, energized in the following manner: Upon closure of the Down push button contact I46,

, current. is suppliedto relay D through acircuit cannotbe completed. (It will beunderstood that normally only one of pawls 68,.61 will thus be preventedfrombeing swunggupwardly by itssolenoid.) However,, a circuit will becompleted from line LI through p sh, button contact ,I 46, contact D3; which awill then be closed, normally closed contacts PI, relay coil U, overload contacts OLI, conductor I48, safety limit switch LSS, to L3. Energization of, relay U willv cause the motor II8 to start. and commence forcing the plungers I6 and I7 upwardly. This will continueuntil the strain on the pawl 66 or 67 is released, whereupon its associatedsolenoid 78 or [8 will pull the pawl upwardly and close switches 82 or 88. When this occurs, relay coil 1? is energized through a circuit traced as follows: From LI push button contacts I46, closed contactsDB, conductor I58, relay coil P, switches 82 and 83, down limit switch LSD, contacts UA2,, conductor I48, safety limit switch LSS, to L3. ,When the coil P is energized, contacts PI, open,.thus deenergizing relay coil U and stopping the motor; ,At the same time the current may now flow through solenoid I32 through the previously described circuit, since switches 82 and 83 are now closed.

When it is desired to adjust the position of the lift by permitting it to descend slowly, the Slow push button; contacts I52 are closed to energize relay coil S through a circuit traced as follows:

From LI, push button contacts I52, coil S, down limit switch LSD, contacts UA2, safety limit switch. LSS to line L3. Closure of contacts S2 resul s in energization of coils I8 and '59, thereby closing switches 82 and ,83, andcompleting a circult to energize solenoid I38 which is traced as follows: From LI, push button contacts I52 conductor I54, slow valve operating solenoid I38, conductor I41, switches 82 and 83, limit switch LSD, contacts UA2, conductor I48, safety limit switch LSS, to line L8. This again assumes that neither of the pawls 66, 6'! is locked in engagement with, its associated ratchet wheel, and that their associated solenoids I8 or, I9 may swing the pawls to their upper positions, closing switches 82 and 83.

However, if either pawl 66 or 61 is in weight bearing engagement with its ratchet wheel, one of the switches 82, 83 may be open, and under thesecircumstances the energization of relay coil S results in the closure of contacts S3 and energization of relay coil U. Energization of relay coil U in the manner previously described will re sult in energization of the motor II8 to raise the lift sufficiently to relieve either of the pawls .68 or 67 of its weight carrying engagement with its associated ratchet wheel. As soon as this occurs, both of, the solenoids l8 and I8 will be capable of closing switches 82 and 83, and this will permit energization of relay coil P through a circuit traced as-follows: From LI, through Slow push button contacts I52, now closed, contacts S8, relay coil P, closed switches 82 and 83, closed limit switch LSD, closed contacts UA2, conductor I48, and safety limit switch LSS, to line L3. Energization of relay coil P will result in opening its contacts PI and thereby break the circuit supplying current to relay coil U, with the result that the motor II8 will again be deenergized and the lift may descend at a rate determined by the size of the restriction I42. This may occur because valve I 40 will then be opened by its solenoid I38, the latter being energized through acircuit which may be briefly traced as follows: From LI,

push button .contactor I52, conductor I54, solenoid I38, conductor I41, closed switches '22, 83 LSD, and UA2, conductor I 48, and safety limit switch LSS, to line L3.

From the foregoing, it will appear that the pawls B8 and 87 are in condition for engagement with their, ratchet wheels. 58 1 ancla59, respective- 1y, at all times, except when either the Down push button or the Slow push button is depressed. Since, in the particular apparatus disclosed herein, the radiation emitting apparatus 90 is'utilized for the treatment of a patient lying beneath it, and since this radiation emitting apparatus may weigh in the order of 18 tons, it will be appreciated that the provision of adequate safety means to prevent undesired lowering of the lift is of extreme importance.

It will be clear that when the beam reaches the lower limit of its stroke, limit switch LSD is opened, thus opening both' possible circuits through the valve controlling relays I32 and I38.

Likewise, when the Up push button is depressed, the relay coil UA is energized, and contacts UA2 are opened so that accidental simultaneous depression of either the down push button contactors I46 or the slow push button contactors i52 cannot have any effect.

While we have shown and described a preferred embodiment of our invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles of the invention. We therefore desire, by the following claims, to include within the scope of the invention all such variations and modifications by which substantially the results of our invention may be obtained through the use of substantially the same or equivalent-means.

We claim:

1. A hydraulically operated lift comprising a pair of spaced parallel cylinders; plungers reciprocable in said cylinders; a beam connected to the upper ends of the plungers; a pair of sprockets secured together and mounted for rotation at each end of the beam; 3. pair of chains to insure translatory movement of the beam, each chain having one end anchored above one end of the beam, meshing with one of each pair of sprockets, and having its other end anchored below the other end of the beam; a ratchet wheel rigidly connected to one of the pairs of sprockets; a pawl cooperable with the ratchet wheel to prevent rotation thereof in the direction it rotates as the beam is lowered; a solenoid which when energized tends to disengage the pawl; and remote switch and circuit means for controlling the energization of the solenoid.

2. The combination set forth in claim 1, in which there is an electromagnetically operated valve to control the discharge of hydraulic fluid from the cylinders, and in which the remote switch means controls the energization of both the solenoid and the electromagnetically operated valve.

3. The combination set forth in claim 2, in which is. included an electric motor, a pump driven thereby, conduits connecting the pump 5. In a hydraulic lift mechanism having a cylinder, a plunger reciprocable in the cylinder, load supporting structure carried by the plunger; the combination of a pawl and ratchet mechanism V operable to prevent lowering of structure;. an

electric motor; a pumpdrivemth'er'eby to supply hydraulic fluid under pressure to the cylinder; an electromagneticallyloperated valve. to .control the discharge of hydraulic fluid from the cylinder; a manually operableswitch and an electric circuit to control thesupply of current to the electromagnetically operated valve; and a second switch operable by the pawl and ratchet mechanism to preventcompletion of said circuit whenever the pawl is engaged with the ratchet.

6. In a two-post liftmechanism, the combination of a pair of cylinders each having a plunger reciprocable therein, a load carrying beam connecting the upper ends of said plungers, a pair of rigidly connected sprocket wheels mounted for rotation at the upper end of each of the plungers, a pair of chains each having one end anchored above the upper limit of travel of one of the plungers and its other end anchored below'the lower limit of travel of the otherplunger, said chains being enmeshed with said sprockets in a manner to cause equalization of the rate of the upward and downward travel of the plungers, a pair of ratchet wheels rigidly secured to one of the pairs of sprockets, pawls respectively engageable with the ratchet wheels in a manner to prevent rotation of the sprocket wheels in the direction in which they rotate upon the downward movement of the plungers, a solenoid for disengaging the pawls, a pair of switches respectively operated by the pawls when they have been released from engagement with their ratchet wheels, a manually operable switch, and means comprising a circuit including said pawl operated switches in series to cause hydraulic power fluid to be supplied to the cylinders upon operation of the manually operable switch whenever said pawl operated switches are open and to effect discontinuance of the supply of the hydraulic power fluid to the cylinders after said pawl has been freed from engagement with its ratchet wheel by its solenoid and has effected closure of both of said pawl operated switches.

7. In a two-post lift mechanism, the combination of a pair of spaced cylinders each having a plunger reciprocable therein, a beam connecting the upper ends of said plungers, a pair of rigidly connected sprocket wheels mounted for rotation at the upper end ofeach of the plungers, a pair of chains each having one end anchored above the upper limit of travel of one of the plungers and its other end anchored below the lower limit of travel of the other plunger,

- said chains being enmeshed with said sprockets in a manner to cause equalization of the rate of the upward and downwardtravel of the plungers, a ratchet wheel rigidly secured to one of the pairs of sprockets, a pawl engageable with the ratchet wheel in a manner to prevent rotation of the sprocket wheels in the direction in which they rotate upon the downward movement of the plungers, a solenoid for disengaging the pawl, a switch closed by the pawl when it is moved from engagement with the ratchet'wheel by the operation of the solenoid, a source of a hydraulic fluid under pressure, and a control circuit including said switch to cause hydraulic power fluid from said source ,to be supplied to the cylinders upon manual operation of a contactor in the control circuit whenever said pawl operated switch is open and to effect discontinuance of the supply of the hydraulic power fluid to the cylinders after said pawl has been freed from engagement with its ratchet wheel by its solenoid and has efifected closure of said switch.

8. In a lift structure, a cylinder; a plunger reciprocable in the cylinder; a latch normally operating to prevent downward movement of the plunger; a solenoid connected to the latch to release the latter when the solenoid is energized; a switch operated by the latch when it is moved to releasing position by the solenoid; a source of hydraulic fluid; an electric motor and pump driven thereby connected to supply hydraulic fluid from the source to the cylinder; an Up switch manually operable to energize said motor; a Down switch; a valve controlling the discharge of hydraulic fluid from the cylinders; electromagnetic means for operating said valve; a circuit including said "Down switch, said electromagnetic means, said latch operated switch, and the source of electrical energy, to effect opening said valve whenever said latch operated switch and said Down switch are closed at the same time; and an additional circult including said Down switch for causing energization of said motor until said latch has operated its associated switch.

9. In a lift structure, a cylinder, a plunger reciprocable in the cylinder, a latch normally operating to prevent downward movement of the plunger, a solenoid connected to the latch to move the latter to unlatched position when the solenoid is energized, a first switch closed by the latch when it is moved to unlatched position by the solenoid, a source of hydraulic fluid, an electric motor and pump driven thereby connected to supply hydraulic fluid from the source to the cylinder, a second switch manually operable to energize said motor, a third switch, a valve controlling the discharge of hydraulic fiuid from the cylinders, electromagnetic means for operating said valve, a circuit including said third switch, said electromagnetic means, said second switch, and the source of electrical energy, to effect opening said valve whenever said latch operated switch and the third switch are closed at the same time, and an additional circuit including and controlled by said third switch for energizing said motor until said second switch is opened by the disengagement of the latch.

10. In a lift mechanism comprising a cylinder and plunger reciprocable therein, the combination of a latching mechanism normally opera: ble to hold said plunger against downward movement, a releasing solenoid connected to the latching mechanism, a motor and pump driven thereby to supply hydraulic fluid under pressure to said cylinder, an electromagnetically operated valve controlling the discharge of hydraulic fluid from the cylinder, manually operable switch and circuit means to eifect energization of said electromagnetically operated valve to open the latter and to energize said solenoid, means in said circuit means to prevent energizetion of said electromagnetically operated valve upon operation of said switch whenever the latching mechanism is effective and to cause energization of the motor until the latching means is released and thereupon to discontinue energization of said motor.

11. In an elevator having a load supportand means for raising and lowering it, the combination of means for insuring translatory movement of the load support, said means including a part which must rotate in a certain direction as the load support moves downwardly, a pawl and ratchet mechanism connected to said part to prevent downward movement of the load support when the pawl is in engagement with the ratchet, control means operable to effect lowering of the load support, and means controlled by the pawl and ratchet mechanism to cause initial elevation of the load support suflicient to release the pawl from its ratchet and thereafter to effect lowering of the load support.

12. In an elevator having a load support and means for raising and lowering it, the combination of means for insuring translatory movement of the load support, said means including a part which must rotate in a certain direction as the load support moves downwardly, a ratchet wheel rigidly secured to said part, a pawl cooperable with the ratchet wheel to prevent rotation of said part in said certain direction, control means operable to a. position to cause lowering of the load, control means to move the pawl from ratchet engaging position, means operable by the control means to cause initial upward movement of the load support, and means operated by the pawl upon movement to a position in which it is free from the ratchet wheel to render said control means eifective to lower the load support.

JOHN B. HARRISON. LAWRENCE F. JASEPH.

No references cited. 

